1. Field of the Invention
The present invention relates to an explosive ink formulation which is stable, free flowing, and can be built up into fire train structures by deposition as nano- and micro-scale patterns using ink jet printers.
2. Related Art
Energetic munitions, such as flares, missiles, military ordinance, etc generally require three distinct components: first, an initiator, second, an explosive train to amplify the output from the initiator, and to ignite the third component, a main output charge, which can be a high explosive, a pyrotechnic, or a propellant. Generally initiators are manufactured of primary explosives (e.g., lead styphnate and the like) which possess relatively low explosive output; but, are highly sensitive explosives that may detonate in response to a small “insult.” The explosive train is generally manufactured of secondary explosives which possess a higher explosive output than the initiator; but, are of lesser sensitivity, requiring a strong shock to detonate—a shock which is provided by the initiator. With the relatively recent emergence of smart weapon systems, such as Micro-Energetic Initiators (MEIs) for Micro Electro-mechanical Mechanisms (MEMs) fuze devices, that are much lighter, smaller, and more survivable than classical initiation devices—the need exists for correspondingly smaller, more precise, explosive trains. Such explosive trains, that contain very small (i.e. microliter) volumes of secondary explosives cannot be manufactured using the standard methods of press-loading or cast loading (whether using melt-cast or cure-cast techniques).
U.S. Pat. No. 7,052,562, Stec et al, discloses a method for loading secondary crystalline energetic materials, such as CL-20, HMX, RDX, TNAZ, PETN, and NNS, into small volume loading holes which form a firing train—the crystalline energetic material being in the form or a slurry or paste in a mixed ethanol and ethyl acetate solvent system, with a polymeric binder incorporated therein as a latex suspension or an emulsion. This slurry or paste is further disclosed as being loaded into the small volume loading holes by direct physical means, such as by (1) placing the slurry or paste onto a blade and wiping that blade over the fixture to force the slurry or paste into the loading holes in the fixture, or (2) placing the slurry or paste into a pipette or syringe and forcing the slurry or paste through the orifice thereof into the loading holes, or (3) using a pump to force the slurry or paste into the loading holes. These mechanical means do not lend themselves to the application/delivery of a finely detailed fire train.
U.S. Pat. No. 7,052,562, further discloses that while it has been known that ink jet printing can accurately deliver small volumes of material—such technology has been dismissed as unsuitable for the deposition of the subject small volume explosive fire trains, for two reasons. First, most inks used for ink jet printing are dye-based, i.e. the colorant dye is dissolved in the fluid medium—which has until now not been conceived as possible with an energetic component—and; although there are pigment-based ink jet inks available, wherein the colorant is an undissolved crystalline material, such undissolved solids can negatively affect ink jet mechanisms. Secondly, in piezoelectric discharge drop-on-demand ink jet printing, which is the most relevant ink jet method, the droplets of ink are subjected to a piezoelectric discharge, as well as, elevated pressure and temperature; which combination of discharge, temperature, and pressure are a safety hazard in combination with undissolved particulate energetic material.
Published U.S. Patent Application 2006/0243151, to Vine et al, discloses a relatively insensitive slurry explosive ink formulation which can be directly printed onto a substrate using a multiplicity of techniques, such as, screen printing or rotary gravure printing techniques, brushing, dipping or spraying, as well as, by using ink jet or dot matrix printers. The slurry explosive ink formulation disclosed comprises a binder, at least one metal, such as aluminum, titanium or iron; at least one non-metal from Group III or IV or a metal oxide where the metal and non-metal particles are 10 microns or less in diameter; but, typically the upper limit for the particle size for the metals is of the order of one to two microns, while for the non-metals it is of the order of 5 microns. Such slurry explosive ink formulations may clog an ink jet printer's nozzles—as will any slurry's having particles with a diameter greater than 200 nano-meters. And, importantly, any such use of an ink jet printer is disclosed solely for applying an initiator, which initiator is used in conjunction with an electrical triggering device, e.g. an adjacent heating element.
Thus there is a need in the art for a non-slurry (i.e. solution) material and technique to accurately lay down a finely detailed secondary explosive structure in a fire train pattern, on various substrates, in very small volumes, e.g. part of a MEMs fuze—to amplify the output from the initiator and to ignite the main output charge—for use in smart weapon systems and the like.